The present invention relates to a process for forming a semiconductor device and, more particularly, to a process for forming multi-layer interconnections.
Multi-layer interconnections have become indispensable as the large scale integration of semiconductor integrated circuits advance. To contact the upper interconnection layers with a substrate when the interconnection layers are ordinarily formed in a multi-layer configuration, it is necessary to form via holes in a thick insulating film laminated with a plurality of layers. This causes the disconnection of the upper interconnection layers at the stepwise difference of the via hole. The disconnection of the interconnections tends to occur particularly when a directional dry etching process such as reactive ion etching (RIE) is used for microminiaturization. This is because the via hole formed by the RIE process has an abrupt step at the side wall.
As a process for preventing the disconnection of such multi-layer interconnections the following process is employed. A first interconnection layers is formed through a first insulating film on a semiconductor substrate formed with a circuit element such as a doped layer. The first interconnection layers is contacted with the substrate through the via holes formed at the first insulating film. At this time, via holes for connecting second interconnection layers formed layer is simultaneously formed in addition to the via holes for contacting the first interconnection layers with the substrate in the first insulating film. An auxiliary interconnection layer contacting the substrate through the via holes is formed on the first insulating layer simultaneously with the first interconnection layers. Subsequently, second interconnection layers are formed through the second insulating film on the substrate formed with the first interconnection layers. The second interconnection layers are contacted with the auxiliary interconnection layers through the via holes formed at the second insulating film. It is necessary to displace a certain degree of distance from the via hole positions for contacting the second interconnection layers with the auxiliary interconnection layers to the via hole positions for contacting the auxiliary interconnection layers with the substrate. This is because an irregular surface increases when the via hole positions are superposed.
According to this process, it is not necessary to engrave deep via holes passing through the first and second insulating film. As a result, it can prevent to a certain degree the disconnection of the second interconnection layer.
However, according to this process, two via holes are necessary at the displaced position for connecting the second interconnection layer with the substrate, and the integration of the integrated circuit decreases.